1. Technical Field
The present invention relates to an aerosol spray apparatus and a method of forming a film using the aerosol spray apparatus.
2. Description of the Related Art
A conventional powder spraying process uses a method, in which powder is deformed by plastic deformation and the contact between them is tighter by melting the powder in a high-temperature, high-pressure environment, or by using a large impulse being generated when the powder strikes a board. This method has been applied to a structure, such as a ship and an automobile, and a coating on both the inner and outer surfaces of a tube, so as to improve the abrasion resistance and thermal endurance.
A research is currently underway to apply the powder spraying process to electronic components. Particularly, a variety of attempts have led to new applications that may be used for film formation on a board and chip manufacturing, which are key technologies for smaller size.
A coating layer formed by the conventional physical vapor deposition (PVD) or chemical vapor deposition (CVD), which are well-known thin-film processes, has a tendency to crack or delamination when the layer's thickness becomes at least a few micrometers.
On the other hand, a thermal spraying process can provide a coating with a thickness of at least a few hundreds micrometers at high speeds. However, pores may occur in a coating layer. Furthermore, some of potential problems with the thermal spraying process are as follows: particles may be vaporized or the chemical composition thereof may be changed while being exposed to high temperatures, an amorphous mass may be formed due to rapid cooling of the particles, there may be cracks formed on a surface of the coating layer, and adhesion between the coating layer and a board may be decreased. Although the thermal spraying process can provide a thick coating at high speeds, it still has some drawbacks, in which it is hard to control the coating thickness and the coating is rough.
A potential problem with an electrostatic powder impact deposition (EPID) process is that particles, such as carbons and metal particles, which are easily charged electrically, can be coated only and other particles, for example, ceramic particles, cannot be coated. Although this process may provide a coating with a thickness of a few micrometers, it may not be able to produce a coating with a thickness of a few tens micrometers. Moreover, the coating layer is formed with a crystalloid mass that is different from an amorphous mass and raw powder.
If the microstructure of a coating layer formed in a gas deposition (GD) process is examined, it may be noticed that nano-particles used as raw powder are stacked and deposited, and thus using ultrafine particles can be a key technical factor. However, since metal ultrafine particles are easily oxidized, an additional process is required. Nevertheless, it is hard to maintain the desired degree of vacuum and check the purity of the gas being used, during the raw material preparation process and coating process.
As alternatives to the conventional processes described above, a cold spray process and an aerosol deposition process may solve the potential problems caused by the thermal spraying process. However, these processes still have a drawback, in which a thin board or chip may not be implemented due to the large impulse being generated when the powder strikes the board.
Furthermore, due to the closed system in a low-temperature environment, the flexibility and economy of the process may be degraded. Moreover, the process may be limited since there are restrictions on the type and size of powder being used and the size of diameter, depending on powder injection methods.